1. Field of the Invention
The present invention relates to a hydraulic shovel provided with main boom, stick boom, bucket or other operation machine and, especially, to a hydraulic shovel ensuring the operation efficiency or the security during the crane work using a hoisting hook.
2. Description of the Related Art
Conventionally, the hydraulic shovel has been used for earth and sand excavation, transportation or various other operations. A hydraulic shovel 1xe2x80x2 shown in FIG. 12 comprises a travel body 2xe2x80x2, a revolving frame 3xe2x80x2 mounted on the travel body 2xe2x80x2 to be rotatable about the vertical axis, and an operation machine 4xe2x80x2 fitted to the revolving frame 3xe2x80x2. The operation machine 4xe2x80x2 comprises a main boom 6xe2x80x2 vertically rising and descending by a not shown main boom cylinder attached substantially to the center of the revolving frame 3xe2x80x2, a stick boom 8xe2x80x2 vertically swinging by a not shown stick boom cylinder attached to the main boom 6xe2x80x2 taking the distal end of the main boom 6xe2x80x2 as fulcrum, and a bucket 11xe2x80x2 vertically swinging by a not shown bucket cylinder attached to the stick boom 8xe2x80x2 through a pair of right and left links 10xe2x80x2 taking the distal end of the stick boom 8xe2x80x2 as fulcrum.
In addition to a not shown engine loaded near the rear section of the revolving frame 3xe2x80x2, a variable capacity type pump (not shown also) driven by the engine, and a plurality of command valves (not shown also) driving a plurality of operation cylinders of the operation machine 4xe2x80x2 by selectively supplying hydraulic oil discharged from the variable capacity type pump are provided. The command valve is connected in correspondence to the operation cylinder of the operation machine 4xe2x80x2. A plurality of not shown command levers for changing over independently the plurality of command valves are disposed in an operator cabin 3axe2x80x2 disposed at a position shifted to the right or to the left from the front center of the revolving frame 3xe2x80x2.
A bottom section of the main boom cylinder is attached to the revolving frame 3xe2x80x2, and a piston rod thereof is attached to the main boom, and the main boom 6xe2x80x2 vertically rises and descends by this main boom cylinder. A bottom section of the stick boom cylinder is attached to the main boom 6xe2x80x2, and a piston rod thereof is attached to the stick boom 8xe2x80x2. The stick boom 8xe2x80x2 swings vertically by the stick boom cylinder taking the distal end of the main boom 6xe2x80x2 as fulcrum. A bottom section of the bucket cylinder is attached to the stick boom 8xe2x80x2, and a piston rod thereof is attached to the link 10xe2x80x2 between the stick boom 8xe2x80x2 and the bucket 11xe2x80x2, and the bucket 11xe2x80x2 vertically swings by the bucket cylinder attached by means of the pair of right and left links 10xe2x80x2. The hydraulic shovel 1xe2x80x2 excavates the ground surface to a desired depth, transports excavated earth and sand to the dumping position and dumps the same.
On the other hand, there is a hydraulic shovel 1xe2x80x2 capable of crane work in addition to earth and sand excavation, transportation and the like. This kind of hydraulic shovel has, as shown in FIG. 12, a hoisting hook 12xe2x80x2 for lifting/hanging a load, fixed swingably to the back face side of the stick boom 8xe2x80x2 through a link attachment fixing pin 11bxe2x80x2 of the bucket 11xe2x80x2, and provides the distal end of the stick boom 8xe2x80x2 with a crane function. In order to prevent the bucket 11xe2x80x2 and the hoisting hook 12xe2x80x2 from interfering during the crane work, the bucket cylinder is extended to the maximum excavation position of the bucket 11xe2x80x2, stopped at a state where the scooping face side of the bucket 11xe2x80x2 is most retracted to the stick boom 8xe2x80x2 side, and the crane work is performed by the hoisting hook 12xe2x80x2 with this stopped posture.
In addition, a hydraulic shovel provided with another crane mechanism is disclosed, for example, in Japanese Utility Model Publication No. 58-11826. According to the hydraulic shovel disclosed in this Publication, a pair of winches are provided on the back of a main boom. A pair of first pulleys are supported by an stick boom support shaft for supporting rotatably the distal end of the main boom and a stock boom, while a pair of second pulleys are supported by the stick boom top pin. Two wires of respective winch are led inside the main boom and stick boom, wound around respective first and second pulleys, wound around a pair of third pulleys supported by a bracket of the hoisting hook, and the distal end of the wire is fixed to the stick boom. The hoisting hook is hung and supported at the stick boom bottom side through the wire, and the hoisting hook moves vertically by taking in/out the wire by the winch.
In order to prevent the bucket and the hoisting hook from interfering during the crane work, the bucket cylinder is retracted to the maximum dumping position of the bucket while being maintained at a posture where the bucket is most damped to the stick boom back side, and the crane work is performed by the hoisting hook with this posture. When the hoisting hook is not in use, the hoisting hook is hung and engaged by a hanging bar disposed inside a forked section of the stick boom by taking up the wire by the winch, and the hoisting hook is housed in the stick boom forked section.
During excavation or transportation of earth and sand, with the hoisting hook housed, the main boom cylinder and stick boom cylinder are operated to swing vertically the main boom and stick boom respectively and, at the same time, the bucket cylinder is operated for nodding the bucket vertically at the distal end of the stick boom. The hydraulic shovel excavates the ground surface to a desired depth, transports excavated earth and sand to the dumping position and dumps the same.
Generally, the conventional hydraulic shovel operates the main boom in the rising direction by elongating the main boom cylinder, and operates the main boom in the descending direction by retracting the same. Even when the main boom is erected, as the gravity center of the operation machine comprising main boom, stick boom and bucket is positioned forward of the equipment, an effort in the retraction directing for descending the main boom is applied to the main boom cylinder, thereby generating a hold pressure at the bottom side thereof at all times. Therefore, if a hydraulic oil hose connected to the main boom cylinder bottom side is broken by an external force, the hold force by the main boom cylinder is lost, and the main boom swings suddenly in the descending direction. Ordinarily, a fall prevention valve maintaining the inner pressure of the bottom side of the main boom cylinder is fitted in order to avoid this sudden swinging.
Moreover, the hydraulic shovel swings the stick boom downward by elongating the stick boom cylinder taking a linkage section with the main boom as fulcrum, and swings the stick boom upward by retraction operation. For example, during the transition from excavation to dumping operation, if a hydraulic oil hose connected to an oil chamber in the head side of the stick boom cylinder is broken by an external force, the hold pressure by the stick boom cylinder is lost, and the stick boom swings suddenly downward with the bucket. It is a common practice that a fall prevention valve is fitted to the head side of the stick boom cylinder in order to avoid this sudden swinging.
During the excavation of earth and sand, the main boom cylinder and stick boom cylinder are operated to swing the main boom and stick boom up and down respectively, and at the same time, the bucket cylinder is operated to nod the bucket at the distal end of the stick boom. An operation range of the distal end of the stick boom section of this time is within a rotation range from the vertical posture of the stick boom as it swings downward, to a swinging upper limit position of the equipment forward side, and a force in the retraction direction is always applied to the bucket cylinder and a hold pressure is generated at the bottom side, because the bucket cylinder is extended during the excavation.
During the transportation of excavated earth and sand to the dumping position, the bucket cylinder is extended, and it transports to the dumping position with the bucket retracted to the stick boom side and stopped (maximum excavation posture). In this case, due to the upper swing of the stick boom, the hold pressure becomes maximum at the beginning of transportation, and decreases gradually as it approaches the dumping position.
During the excavation, for example, if a hydraulic oil hose connected to an oil chamber in the bottom side of the bucket is broken by an external force, as falling of the bucket does not occur, it is unnecessary to provide a fall prevention valve. Even if the hydraulic oil hose is broken during the transport to the dumping position, at most earth and sand in the bucket fall, hardly affecting the periphery. Therefore, ordinarily, it is unnecessary to provide a rotation prevention valve in the oil chamber of the bucket cylinder bottom side.
On the contrary, during the dumping, as the bucket cylinder is operated to the retraction direction, the weight of the bucket and the weight of earth and sand generate hold pressure at the head side. At this time, for example, if a hydraulic oil hose connected to an oil chamber in the head side of the bucket cylinder is broken by an external force, the hold pressure of the bucket cylinder is lost all of a sudden, and the bucket swings suddenly downward, and may damage equipment and the like in the periphery.
Concerning the operation range of the distal end of the stick boom section for lifting a load also, as mentioned above, the hydraulic shovel stick boom is limited within the rotation range from the vertical posture to the swinging upper limit position at the equipment forward side. Therefore, as in the excavation or transportation operation, a hold pressure is always generated at the stick boom cylinder head side during the crane work.
At the dumping position, the weight of the bucket generates a hold pressure at the head side, as the bucket cylinder is operated toward the retraction, during the transition of the bucket maximum excavation posture to the dumping posture. For example, if the hydraulic oil hose connected to the oil chamber in the head side of the bucket cylinder is broken by an external force, the hold force of the bucket cylinder is lost instantaneously, and the bucket rotates suddenly downward. However, the conventional bucket cylinder is not provided with a rotation prevention valve for avoiding such a sudden swinging.
In the aforementioned type of hydraulic shovel provided with a cane function as shown in FIG. 12, as for the operation range of the distal end of the stick boom section for lifting a load, as mentioned above, the stick boom of the hydraulic shovel is limited within the rotation range from the vertical posture to the swinging upper limit position at the equipment forward side. Therefore, as in the excavation or transportation operation, a hold pressure is always generated at the stick boom cylinder head side during the crane work.
When a load is being lifted within the rotation range from the stick boom vertical posture to the swinging upper limit position at the equipment forward side, as the stick boom swings upward by operating the stick boom cylinder in the retraction direction, for example, if the hydraulic oil hose connected to the oil chamber in the head side of the stick boom cylinder is broken by an external force, the hold pressure of the stick boom cylinder head side is lost instantaneously, and the stick boom rotates suddenly downward. Accordingly, the lifted load swings largely taking the distal end of the stick boom as fulcrum. A rotation prevention valve fitted to the aforementioned stick boom cylinder head side prevents such event from occurring.
When a load is lifted, especially in the case that the hoisting hook is provided on the back side of the stick boom, in order to prevent the bucket and the hoisting wire from interfering, the bucket cylinder is extended to its extension limit to hold the bucket at its most retracted position. As a result, the maximum hold pressure is generated at the bucket cylinder bottom side.
When the hydraulic oil hose connected to the oil chamber in the bucket cylinder bottom side is broken, also, the bottom side hold force is lost instantaneously as for the stick boom, and the bucket rotates suddenly downward. However, the bucket cylinder is not provided with a rotation prevention valve for avoiding such a sudden swinging.
If the crane work, excavation or other operation can be performed with the stick boom rotated up to a front immediate proximity position of the equipment, the operation can be performed before the operatorxe2x80x2s eyes, and it is further preferable in respect of the operation efficiency. However, in the state of art, it is difficult to improve the operation efficiency, because the stick boom can not move to the front immediate proximity position of the equipment, as the stick boom rotation from upward to downward is limited forward than the position corresponding the stick boom vertical posture. In addition, when a load is to be lifted, the hoisting hook is obliged to move within the stick boom rotation range, as the stick boom rotation range is limited. As a result, the crane work is performed at the position far from the equipment because the stick boom rotation range is limited, deteriorating the crane work efficiency remarkably.
Beside, when the crane work is to be performed by the hydraulic shovel provided with crane function disclosed in the aforementioned Publication, in order to prevent the bucket and the lifting wire from interfering, the bucket cylinder is retracted to its retraction limit to hold the bucket at its most dumped position. As a result, the maximum hold pressure is generated at the bucket cylinder head side.
In the state where this bucket dumping position is maintained, for example, if the hydraulic oil hose connected to the oil chamber in the head side of the bucket cylinder is broken, the hold pressure of the bucket cylinder head side is lost instantaneously, and the bucket rotates freely downward, applies a large impact to the lifting wire, if a load is being lifted, and may damage or cut the wire. As the result, the hoisting hook or the wire with its load swing largely or fall.
In addition, the distal end of the stick boom disclosed in the aforementioned Publication, supports rotatably one end of each of a pair of landcells of the bucket by a stick boom top pin provided inside the forked section separated right and left and, at the same time, hangs the hoisting hook through two wires wound around a pair of second pulleys provided on the stick boom top pin. Consequently, the distal end of the stick boom section should be strong enough to resist the weight of hoisting hook itself, the load weight or others. Moreover, it is preferable to house the hoisting hook without requiring manual work during the transition from crane work to excavation operation.
The present invention has been achieved in view of these conventional problems. An object of the invention is to provide a hydraulic shovel allowing to prevent a stick boom and a bucket from free fall, by ensuring a hold force of a stick boom cylinder and a bucket cylinder, to enlarge the operation range of an operation machine.
The stick boom downward rotation limit is restricted to the position of its vertical posture, because, when the stick boom rotates to the equipment front immediate proximity position, the stick boom rotates downward to the vertical posture position, thereafter, rotates forward and upward, and at this time also, it becomes necessary to maintain the hold pressure at the cylinder bottom side. However, in the state of art, the stick boom cylinder hold pressure is secured only at the head side.
It is preferable that the hydraulic shovel provided with crane function can be operated at the equipment immediate proximity position not only during the excavation or transportation, but also during the crane work and, therefore, it is desirable to provide the corresponding oil chamber side with rotation prevention means of main boom, stick boom and bucket, so as to maintain the hold pressure securely, even when the maximum hold pressure is applied to respective cylinders of main boom, stick boom and bucket and, at the same time, to maintain the hold pressure thereof, even when the hydraulic oil hose is broken.
The present invention provodes a hydraulic shovel, comprising a main boom rising and descending on a revolving frame, a stick boom linked to the distal end of the main boom and swinging in a vertical direction, and a bucket attached to the distal end of the stick boom and swinging similarly in the vertical direction, wherein the main boom, the stick boom and the bucket are respectively operated independently by operation cylinders; and stick boom rotation prevention means for preventing the stick boom from free fall by maintaining a bottom side hold pressure is provided on a bottom side of the cylinder for the stick boom.
The stick boom cylinder extends until the stick boom rotates downward and attain the vertical position, and at this time, the stick boom hold pressure is always generated at the stick boom cylinder head side. Therefore, conventionally, the rotation prevention valve has been fitted to the stick boom cylinder head side. However, in excavation work or crane work, when the stick boom rotates from the vertical posture to the rotation upper limit position at the equipment rear side, the stick boom cylinder continues to extend and, at the same time, the stick boom hold pressure shifts to the bottom side. Consequently, it is necessary to provide the stick boom cylinder bottom side also with rotation prevention means as the head side as the case of the present invention, in order to rotate the stick boom to the equipment rear side rotation upper limit position and hold the same.
In the present invention, the stick boom rotation prevention means is directly fixed to the bottom side of stick boom cylinder, and even if the hydraulic oil hose connected to the stick boom cylinder bottom side is broken and the bottom side hydraulic pressure is lost during the rotation of the stick boom toward the rotation upper limit position at the equipment rear side, the stick boom rotation prevention means cuts off the cylinder bottom side oil chamber from the exterior oil passage, and maintains the hold pressure of the bottom side oil chamber.
In addition, for example, detecting the rupture of the hydraulic oil hose or the like connected to the bottom side oil chamber, during the operation of a command valve, the command valve may be returned automatically to the non-operation position and, in this case also, the stick boom rotation prevention means maintains securely the bottom side hold pressure, and supply and discharge of the hydraulic oil stop automatically.
The aforementioned composition makes unnecessary to set the stick boom limit operation range as in the prior art, and allows to rotate freely within the equipment forward side and equipment backward side rotation limits including the stick boom vertical posture by the operation of the stick boom cylinder. As a result, the safety is secured, the operation range can be extended, allowing to perform an effective earth and sand excavation and transportation work.
If the rotation prevention means is provided both at the head side and bottom side of the stick boom cylinder, a sudden downward rotation of the stick boom can be prevented, because hold pressure in the cylinder extension direction and retraction direction by the load of the stick boom and excavated earth and sand or the like is supported instantaneously by the rotation prevention means, and the safety can be secured in the extended whole operation range.
On the other hand, when excavated earth and sand are transported to the dumping position, the bucket cylinder is extended, and the bucket is maintained at the maximum excavation posture where the bucket is stopped at the state retracted to the stick boom lower face side. In this case, a force in the cylinder retraction direction is always applied to the bucket and generates a hold pressure at the bucket cylinder bottom side. At this dumping position, the stick boom cylinder is retracted to rotates the stick boom upwards and, at the same time, the bucket cylinder is retracted to shift the bucket from the maximum excavation posture to the maximum dumping posture. In this dumping posture, an extension force is always applied to the bucket cylinder and generates a hold pressure at the bucket cylinder head side.
According to the present invention, similarly as the aforementioned stick boom, it is preferable to fix bucket rotation prevention means directly to the bottom side of a desired cylinder oil chamber, for enabling to support a force in the cylinder extension direction or retraction direction applied by the bucket own weight or the like and, in addition, to prevent the bucket from falling rapidly.
For example, during earth and sand excavation and transportation, the stick boom is rotated vertically not only in the equipment forward side operation range, but also in the whole rotation range including the equipment backward side, and at the same time, the bucket is made to nod vertically by the operation of the bucket cylinder. The aforementioned composition increases the stick boom rotation range compared to the case where the operation is performed only within the rotation range of a stick boom rotating from the vertical posture to the equipment forward side as in the prior art and, in addition, enlarges the bucket excavation rotation range, and increases the excavation range thereof. At the same time, in addition to the functional effect as mentioned before, securer and more effective earth and sand excavation and transportation can be performed, and moreover, the work safety can be enhanced.
Further, in the present invention, bucket rotation prevention means for preventing the bucket from free fall by maintaining the head side hold pressure when the bucket cylinder is retracted is preferably provided at least on the head side of the bucket cylinder.
As the hydraulic shovel disclosed in the aforementioned Publication, the hoisting hook is provided at the stick boom top pin for attaching the bucket and stick boom, and hung from the distal end of the stick boom section. During the crane work, in order to prevent the bucket and the hoisting hook from interfering, the aforementioned bucket cylinder is required to retract to the state where the bucket is most dumped to the stick boom back side (maximum dump position). In this case, the crane work is performed by the hoisting hook with the scooping face side of the bucket faced downward. When the load is lifted, a force in the cylinder extension direction is always applied to the bucket and the maximum hold pressure is generated at the bucket cylinder head side in almost all areas in the rotation range of its main boom and stick boom.
In the present invention, as bucket fall prevention means is directly fitted at least to the head side of the bucket cylinder, even if the hydraulic oil hose connected to the oil chamber in the head side of the bucket cylinder is broken during the crane work, the bucket fall prevention means acts instantaneously, cuts off completely the head side oil chamber from the exterior oil passage, maintains securely the hold pressure of the head side, and prevents the bucket from swinging suddenly downward.
In addition, for example, detecting the rupture of the hydraulic oil hose connected to the bucket cylinder head side, during the operation of the command valve, the command valve may be returned automatically to the non operation position. In this case also, the bucket fall prevention means maintains securely the head side hold pressure, and the hydraulic oil supply and discharge stop automatically.
The hoisting hook is disposed at the stick boom top pin for attaching bucket and stick boom, and hung from the distal end of the stick boom section. During the crane work, the bucket is set in the dumping posture allowing the operator to watch the hook with his/her eyes, and to perform the crane work effectively and safely, without being obstructed to look forward by the bucket.
On the other hand, during earth and sand excavation, the stick boom is rotated vertically by the operation of the stick boom cylinder head side, and at the same time, the bucket is made to nod vertically by the operation of the bucket cylinder. If the bucket fall prevention means is provided both at the head side and bottom side of the bucket cylinder, during the operation at the dump position with the bucket cylinder retracted, or during the operation at the excavation position with the bucket cylinder extended, even if the hydraulic oil hose connected to the hold pressure generation side of the bucket cylinder is broken, the bucket fall prevention means closes the inside of the cylinder completely, and maintains the maximum hold pressure of the bucket cylinder, enabling to support a hold pressure in the cylinder extension direction or retraction direction applied by the bucket own weight, the load of excavated earth and sand or the like, to prevent securely the bucket from falling rapidly, and to enhance the work safety.
For example, during transportation of excavated earth and sand excavation, the bucket cylinder is extended, and the bucket is maintained in its maximum excavation posture where the bucket is stopped at the state retracted to the stick boom under face side. In this case, a force in the cylinder retraction direction is always applied to the bucket and the maximum hold pressure is generated at the bucket cylinder bottom side. At this dump position, the stick boom is rotated upward by retracting the stick boom cylinder, and at the same time, the bucket is shifted from the maximum excavation posture to the maximum dumping posture by retracting the bucket cylinder. In this dumping posture, a force in the extension direction is always applied to the bucket cylinder, generating a hold pressure at the bucket cylinder head side.
When the bucket is shifted from the maximum excavation posture to the maximum dumping posture, even if the hydraulic oil hose connected to the head side of the bucket cylinder is broken, the bucket fall prevention means closes inside of the cylinder completely, and maintains the maximum hold pressure of the bucket cylinder, enabling to support the force in the cylinder extension direction, to prevent securely the bucket from rotating downward suddenly, and to enhance the work safety.
Preferably, in addition to the bucket cylinder, stick boom fall prevention means for preventing the stick boom from freely rotating downward by maintaining a bottom side hold pressure is provided on a bottom side of the stick boom cylinder.
When the stick boom rotates to the equipment front immediate proximity position, the stick boom rotates downward to the vertical posture position, thereafter, rotates forward and upward, and the stick boom cylinder hold pressure shifts from the head side to the bottom side through the vertical posture position. Conventionally, the stick boom rotation range of this side from forward is restricted to the position of its vertical posture, because, the stick boom cylinder hold pressure is secured only at the head side.
However, it is preferable that the hydraulic shovel provided with crane function can be operated at the equipment immediate proximity position not only during the excavation or transportation, but also during the crane work and, therefore, it is desirable to provide the corresponding oil chamber side with rotation prevention means of main boom, stick boom and bucket, so as to maintain securely the hold pressure, even when the maximum hold pressure is applied to respective cylinders of main boom, stick boom and bucket and, at the same time, to maintain the hold pressure thereof, even when the hydraulic oil hose is broken.
The stick boom cylinder extends until the stick boom rotates downward and attain the vertical position, and at this time, the stick boom hold pressure is always generated at the stick boom cylinder head side. Therefore, conventionally, a rotation prevention valve has been fitted to the stick boom cylinder head side. However, in crane work or excavation work, when the stick boom rotates from the vertical posture to the rotation upper limit position at the equipment rear side, the stick boom cylinder continues to extend and, at the same time, the hold pressure of the stick boom shifts to the bottom side. Consequently, it is necessary to provide the stick boom cylinder bottom side also with rotation prevention means as the head side as the case of the present invention, in order to rotate the stick boom to the rotation upper limit position at the equipment rear side and hold the same.
In the present invention, similarly as the aforementioned bucket, the stick boom rotation prevention means is directly fixed to at least the bottom side of the stick boom cylinder, and even if the hydraulic oil hose connected to the stick boom cylinder bottom side is broken and the bottom side hydraulic pressure going to be lost when the stick boom is rotating to the equipment rear side maximum rotation position, the stick boom fall prevention means cuts off the cylinder bottom side oil chamber from the exterior oil passage, and maintains the hold pressure of the bottom side oil chamber.
This means that the crane work can be performed not only in the equipment forward side including the stick boom vertical posture by the operation of the stick boom cylinder, but also at the equipment immediate proximity position. As the crane work can be performed in the equipment proximity, and the positional relationship between the hoisting hook and load can be checked with eyes, the work efficiency can be enhanced considerably. In addition, as the crane work range is enlarged, the crane work in a small site can be performed effectively and safely.
On the other hand, during earth and sand excavation and transportation, the stick boom is rotated vertically by the operation of the stick boom cylinder not only in the equipment forward side operation range, but also in the whole rotation range including the equipment rear side, and at the same time, the bucket is made to nod vertically by the operation of the bucket cylinder. The aforementioned composition increases the stick boom rotation range compared to the case where the operation is performed only within the rotation range of the stick boom rotating from the vertical posture to the equipment forward side as in the prior art and, in addition, enlarges the bucket excavation rotation range, and increases the excavation range thereof.
At the same time, it becomes unnecessary to set the limit of the stick boom operation range as in the prior art, and allows to rotate freely within the equipment forward side and equipment backward side rotation limits including the stick boom vertical posture by the operation of the stick boom cylinder. As a result, the safety is secured, the operation range can be extended, allowing to perform an effective earth and sand excavation and transportation work.
If the stick boom fall prevention means is provided at both of the head side and bottom side of the stick boom cylinder, the hold pressure in cylinder extension direction or retraction direction generated by the load of the stick boom, excavated earth and sand or the like is supported instantaneously by the fall prevention means, preventing the stick boom from rotating suddenly downward, and securing the safety in the enlarged aforementioned whole operation range.
In the aforementioned embodiment of the present invention, if the stick boom top pin is rotatably supported by the distal end of the stick boom, and the base end of the hoisting hook is axially supported by the stick boom top pin, it is preferable that the distal end face opposite to the back face of the stick boom comprises a hoisting hook receiving section having an opening and being capable of housing the hoisting hook; a reinforcement member disposed around the peripheral section of the opening; and an engagement member for engaging a hook section of the hoisting hook by hanging.
Such composition, comprising the reinforcement member for closing the opening peripheral section of the hoisting hook receiving section in the stick boom, can secure a sufficient strength of the distal end of the stick boom. As the hoisting hook can be housed in the hoisting hook receiving section of the stick boom, the bucket and the hoisting hook are prevented from interfering, the hoisting hook does not obstructs anything, and is prevented from hitting and damaging obstacles, and at the same time, earth and sands are prevented from entering the hoisting hook receiving section.
In the present invention also, bucket fall prevention means is fitted to the bucket cylinder head side, and the function during the crane work is not substantially different from the aforementioned function. As mentioned above, during the crane work with bucket back face directed downward, for example, even if the hydraulic oil hose connected to the bucket cylinder head side is broken, the bucket fall prevention means acts immediately, cuts off completely the head side oil chamber from the exterior oil passage, maintains the hold pressure of the head side, and prevents the bucket from rotating suddenly downward.
Further, it is preferable that the hoisting hook is linked to a hook rotation driving mechanism for rotating about the stick boom top pin.
Taking effectively profit of the inside space of the aforementioned main boom and stick boom, a simple structure rotation driving mechanism having a pulley around which wire or the like are wound and an electric motor or the like for operating that pulley together are installed for example in the main boom and stick boom, it is made to work together with the stick boom top pin. The hoisting hook is turned in the normal and reverse direction through the rotation driving mechanism by driving the electric motor. For the transition from crane work to excavation work, the hoisting hook can be housed automatically in the aforementioned hoisting hook receiving section by rotating about the stick boom top pin, without requiring manual labor, or the inverse operation can be performed.